It is desirable to retain heat in hair curlers, and as the microwave oven has become more common in ordinary households, workers in the art have designed curlers to utilize their ready availability. For example, Henderson, in U.S. Pat. No. 4,538,630, fills a substantially cylindrical curler with a lossy dielectric material, such as a ferrite or zirconium dioxide. Graves, in U.S. Pat. No. 5,676,871, also proposes use of a lossy dielectric material in one variation of her invention. Switlicki, in U.S. Pat. No. 4,710,609, fills the curler cavity with a wicking material and water, leaving a vent for expanding water to escape if the temperature becomes too high in the microwave. In U.S Pat. No. 4,743,726, Hughes adds a wax core to serve as a kind of heat sink.
In U.S. Pat. Nos. 4,952,360 and 5,030,820, Gibbon constructs a microwavable hair curler from a composition including a polyorganosiloxane gum, a particulate electromagnetic absorptive material, a filler, and a catalyst. The preferred absorptive material is zinc oxide; the composition is extruded and cured ('820 col. 2, lines 1-9). A cylindrical curler is filled with a "silicon gel" by Summerville et al in U.S. Pat. No. 5,297,567 for "heat retentive purposes" (col. 3, lines 23-24).
In U.S. Pat. No. 5,456,701, Stout describes a gel contained in a sheath for use in a therapy member--that is, a heat pad. The gel comprises water, a humectant, and a crosslinked water soluble polymer. The humectant is preferably glycerin and the crosslinked water soluble polymer is preferably a crosslinked polyacrylamide. Such a gel is found to retain heat imparted by a microwave oven.